Processes influencing the population dynamics and conservation of African penguins on Dyer Island, South Africa

  • K Ludynia
  • LJ Waller
  • RB Sherley
  • F Abadi
  • Y Galada
  • D Geldenhuys
  • RJM Crawford
  • LJ Shannon
  • A Jarre

Abstract

Dyer Island, South Africa, supported the largest African penguin Spheniscus demersus colony in 1979 (22 655 breeding pairs), but population dynamics of the species have not followed the trends of adjacent colonies in years of high fish abundance or shifts in prey distribution. Less than 1 500 pairs were breeding on Dyer Island in 2013. Available knowledge on demographic parameters was collated and ecological processes were quantified. Juvenile and adult survival probabilities estimated for birds ringed on Dyer Island between 2005 and 2011 were 0.247 (SE 0.06) and 0.545 (SE 0.05) respectively. Juveniles had a high probability (0.918; SE 0.077) of moving away from Dyer Island. Predation by seals and kelp gulls, as well as oiling, are currently important top-down pressures on penguins on Dyer Island. Numbers of birds breeding on the island were negatively correlated with purse-seine catches 20 nautical miles around it. However, it seems that once the colony size is <3500 breeding pairs, the importance of fishing pressure diminishes, suggesting that once a colony has been reduced to a relatively small size, its growth is limited by pressures other than fishing. From the review of available knowledge presented here, we recommend a number of management options that should be tested in a suitable model.

Keywords: ecosystem approach to fisheries (EAF), food availability, multistate capture-mark-recapture model, pressures, seabird conservation

African Journal of Marine Science 2014, 36(2): 253–267

Author Biographies

K Ludynia

Marine Research Institute, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa; Animal Demography Unit, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa

 

LJ Waller
Western Cape Nature Conservation Board, Scientific Services, Hermanus, South Africa
RB Sherley

Marine Research Institute, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa; Animal Demography Unit, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa

F Abadi
Animal Demography Unit, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa; Current address: School of Statistics and Actuarial Science, University of Witswatersrand, Johannesburg, South Africa
Y Galada
Marine Research Institute, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa; Animal Demography Unit, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa; Western Cape Nature Conservation Board, Scientific Services, Hermanus, South Africa
D Geldenhuys

Western Cape Nature Conservation Board, Scientific Services, Hermanus, South Africa

 

RJM Crawford
Animal Demography Unit, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa; Branch: Oceans and Coasts, Department of Environmental Affairs, Cape Town, South Africa
LJ Shannon
Marine Research Institute, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa
A Jarre
Marine Research Institute, Department of Biological Sciences, University of Cape Town, Rondebosch, South Africa
Published
2014-07-30
Section
Articles

Journal Identifiers


eISSN: 1814-2338
print ISSN: 1814-232X